U.S. patent number 6,174,335 [Application Number 09/130,396] was granted by the patent office on 2001-01-16 for alignment guide for slotted prosthetic stem.
This patent grant is currently assigned to Johnson & Johnson Professional, Inc.. Invention is credited to Charles W. Jaggers, Mark Allan Manasas, Pierre S. Ostiguy, Jr., Paul Salvas, Michael S. Varieur.
United States Patent |
6,174,335 |
Varieur , et al. |
January 16, 2001 |
**Please see images for:
( Certificate of Correction ) ** |
Alignment guide for slotted prosthetic stem
Abstract
An alignable orthopedic prosthesis system includes a prosthesis
and an alignment guide. The prosthesis includes a stem having at
least one slot extending along its length. The alignment guide has
an alignment body with a guide surface extending from an end
thereof, namely a key element formed as a blade for engaging and
guiding the slot to orient the prosthesis stem. The alignment body
also fits against a machined bone surface so that the blade is
positioned in a plane that is oriented to guide the stem smoothly
into contact with a recess formed in the bone.
Inventors: |
Varieur; Michael S. (Attleboro,
MA), Ostiguy, Jr.; Pierre S. (Rochester, MA), Jaggers;
Charles W. (Mansfield, MA), Salvas; Paul (Norton,
MA), Manasas; Mark Allan (S. Easton, MA) |
Assignee: |
Johnson & Johnson Professional,
Inc. (Raynham, MA)
|
Family
ID: |
27379396 |
Appl.
No.: |
09/130,396 |
Filed: |
August 6, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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102721 |
Jun 22, 1998 |
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772630 |
Dec 23, 1996 |
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Current U.S.
Class: |
623/22.12;
606/99; 623/908 |
Current CPC
Class: |
A61F
2/4684 (20130101); A61F 2/4607 (20130101); A61F
2230/0008 (20130101); A61F 2002/365 (20130101); A61F
2002/30332 (20130101); A61F 2250/0089 (20130101); A61F
2002/4619 (20130101); A61F 2002/369 (20130101); A61F
2/36 (20130101); A61F 2/30724 (20130101); A61F
2002/30125 (20130101); A61F 2002/3625 (20130101); Y10S
623/908 (20130101); A61F 2/3676 (20130101); A61F
2220/0033 (20130101); A61F 2250/0097 (20130101); A61F
2/367 (20130101); A61F 2230/0006 (20130101); A61F
2002/30617 (20130101); A61F 2002/3071 (20130101); A61F
2002/30884 (20130101); A61F 2002/30828 (20130101); A61F
2002/30594 (20130101); A61F 2/4603 (20130101); A61F
2002/30827 (20130101); A61F 2002/30879 (20130101); A61F
2002/30113 (20130101) |
Current International
Class: |
A61F
2/46 (20060101); A61F 2/36 (20060101); A61F
2/00 (20060101); A61F 2/30 (20060101); A61F
002/32 (); A61B 017/00 () |
Field of
Search: |
;623/18,20,22,23,22.12,23.35,902,908 ;606/86-90,95,96,99 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yu; Mickey
Assistant Examiner: Nguyen; Tram A.
Attorney, Agent or Firm: Nutter, McClennen & Fish,
LLP
Government Interests
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation-in-part of U.S. patent
application Ser. No. 09/102,721 filed Jun. 22, 1998 entitled
Alignment Guide for Fluted Prosthetic Stems, which was a
continuation-in-part of U.S. patent application Ser. No.
08/772,630, filed Dec. 23, 1996 now abandoned.
Claims
What is claimed is:
1. An alignable orthopedic prosthesis system for implantation into
a prepared bone cavity, said system comprising:
(a) a prosthesis including a stem having a proximal portion, a
distal portion, and an axis, with a slot extending along the axis
of the stem, and
(b) an alignment guide including
an alignment handle having an outer shaped surface portion
corresponding to at least a portion of the prepared bone cavity,
and
a guide blade disposed on an inner portion of the alignment handle
and keyed for engaging the slot of the stem, said outer shaped
surface portion being positioned such that when said shaped portion
seats against the prepared bone cavity, the blade is located in a
plane effective to fix rotational alignment of the stem while
allowing sliding insertion, such that the guide blade orients the
prosthesis to seat in a desired orientation in the bone.
2. The prosthesis system of claim 1, wherein the prosthesis
comprises a stem of a prosthetic joint assembly.
3. The prosthesis system of claim 2, wherein the blade comprises at
least one relief portion for reducing binding in the slot.
4. The prosthesis system of claim 2, wherein the blade effectively
fills the cross-section of the slot.
5. The prosthesis system of claim 3, wherein the blade extends
transverse to the stem.
6. The prosthesis system of claim 1, wherein the alignment guide
further comprises means for effecting removal of the guide from the
stem along an axis parallel to or a direction away from the
prepared bone cavity.
7. The prosthesis system of claim 1, wherein the proximal portion
of the stem comprises a proximal geometry shaped to fit said
prepared bone cavity.
8. The prosthesis system of claim 1, wherein the outer shaped
surface portion fits against a cylindrical prepared bone surface to
align the blade along an axis.
9. The prosthesis system of claim 8, wherein the handle and blade
of the alignment guide both extend along said axis.
10. A prosthetic stem system comprising:
(a) a prosthetic stem including a longitudinal axis, a slot
extending along the axis, and an outer surface having at least one
stem surface feature extending along the outer surface in a
substantially longitudinal direction for penetrating and gripping
bone, and
(b) an alignment guide including:
a handle having proximal and distal ends and a longitudinal
axis;
an alignment blade disposed on the distal end of the handle to
releasably engage the slot as a guide surface that extends parallel
to the handle across the longitudinal axis to engage inside slot
surfaces and provide rotational stability to the prosthetic stem
during insertion of the stem into a bone,
said alignment guide being oriented by contact with a prepared bone
surface to guide the slot during prosthesis insertion to fit a
final insertion position.
11. The stem system of claim 10, wherein the stem is fluted.
12. The stem system of claim 10, further comprising a femoral
prosthesis associated with the prosthetic stem, the femoral
prosthesis including a spout, wherein the blade is oriented to be
in a plane aligned with the spout of the femoral prosthesis.
13. The stem system of claim 10, wherein the blade is laterally
disengageable from the stem by movement along the longitudinal axis
of the handle.
14. The stem system of claim 10, wherein the stem is elongated,
substantially cylindrical and implantable within a prepared bone
cavity of a long bone.
15. The stem system of claim 14, wherein the stem forms at least
part of a femoral component for a hip prosthesis.
16. The stem system of claim 15, wherein the stem includes a
proximal spout.
17. The stem system of claim 14 wherein the alignment guide handle
comprises an outer surface shape corresponding to at least a
portion of the prepared bone cavity for orienting the blade.
18. The stem system of claim 14, wherein the slot provides bending
fit of the stem, and the slot tapers wider toward a proximal end of
the slot to reduce binding on the blade.
19. A method for inserting a prosthetic stem into a long bone
comprising the steps of:
(a) preparing a cavity in the long bone;
(b) providing a prosthetic stem having a longitudinal axis, an
outer surface, and at least one stem slot extending along a
longitudinal direction
(c) providing an alignment guide including a handle having proximal
and distal ends, and an alignment blade disposed on the distal end
of the handle and releasably engageable with the slot of the
prosthetic stem, wherein the blade rigidly projects from the handle
so as to fit in the slot and engage the stem to provide rotational
stability to the prosthetic stem
(d) placing the alignment guide at the prepared cavity so as to
orient the blade in a predetermined rotational orientation
(e) engaging the alignment guide blade in the slot of the
prosthetic stem, and
(f) inserting the prosthetic stem into the cavity along the blade,
thus guiding the stem into a final position fitting the prepared
cavity.
Description
FIELD OF THE INVENTION
The present invention relates to an alignment guide for ensuring
proper alignment or orientation of a prosthetic stem in bone.
BACKGROUND OF THE INVENTION
Stems are used in prosthetic joint implants to anchor the implant
in a bone cavity. The bone for receiving the stem is typically
prepared by drilling a hole in the bone and creating an opening
sized and contoured to receive the stem of the implant. The stem is
inserted into a prepared cavity of a bone and a joint bearing
surface attached or coupled to the stem, extends out to the cavity.
Many stems are fluted, i.e., they have distally extending
longitudinal grooves in the stems that provide greater stability
and anchoring of the stem once it is inserted into the prepared
cavity.
Typically, once a fluted stem is inserted into a prepared cavity,
it is extremely difficult to rotate the stem to properly reorient
it. In order to do so the stem must be removed and reinserted which
can damage bone and increase operative time. Typically, the stem is
aligned by marking the bone and the stem and using the marks to
align the stem with respect to the bone. The drawback to this
method is the potential imprecision in the alignment. Because the
landmark on the stem and bone are not in close proximity to each
other, parallax and other problems associated with alignment by eye
may result. Also, the stem may move from its aligned position as it
is inserted.
Accordingly, it is an object of the present invention to provide a
means for aligning a fluted stem of an orthopedic implant prior to
and as it is being inserted into a prepared bone cavity.
SUMMARY OF THE INVENTION
The present invention provides a method and device for inserting a
keyed or fluted prosthetic component in an aligned position into a
prepared bone cavity. The bone is prepared by removing bone
material from the bone canal and by machining an opening of a
predetermined shape in the bone cavity. An alignment guide having
an outer shape conforming with that of the machined opening is
inserted into the bone cavity. The alignment guide also has an
inner shape or key element corresponding to the outer shape of the
fluted stem of the implant that engages the stem, preferably in a
manner which provides contact with a small area of the stem. In a
preferred embodiment the inner shape of the alignment guide
includes notches or grooves for receiving the flutes of the stem.
Another aspect of a preferred embodiment may provide protrusions in
the alignment guide that make contact with certain keyed elements
of the prosthesis to be inserted.
In a preferred embodiment, the alignment guide is formed generally
in a broken circle or circumference to allow flexibility in
removing the alignment guide. The alignment guide further comprises
a means for lifting the alignment guide from the bone cavity once
the stem is inserted through the alignment guide. This means may,
for example, be a tab or protrusion or an opening for inserting a
tool to pry out the guide. In a further embodiment, the alignment
guide includes a guide body that is disposed at the distal end of a
handle.
In a preferred embodiment, once the bone cavity is prepared and the
alignment guide is inserted, a fluted stem of a prosthetic implant
is positioned or oriented with respect to the stem axis and is then
inserted into the alignment guide with the flutes extending into
the notches of the alignment guide. Once the stem is inserted in
the guide, the position or orientation is held true until the stem
is seated into the bone cavity. As the stem is inserted, the flutes
form a path within the bone cavity that the stem will generally
follow during the insertion of the final segment of the stem. Once
this has occurred the alignment guide may be removed by pulling the
tab. The insertion is completed by extending the implant all the
way into the opening until the proximal geometry of the stem is
placed within the machined opening in the bone. This stem proximal
geometry is also of a shape that corresponds to the machined
opening so that the implant fits within the bone cavity.
In another embodiment, the alignment guide keys to the stem by a
blade which fits within a longitudinal slot of the stem to fix its
rotational orientation. The slot is parallel along the central
plane of the spout, and the blade, which rigidly extends from the
guide, is centrally aligned by means of an opposed guide surface
that fits the prepared bone, so as to define an insertion
orientation to guide the proximal geometry of the stem into the
prepared contour. This embodiment is preferably implemented as an
elongated handle, having a proximal grip portion, a blade extending
from the distal end, and a middle shoulder which fits the prepared
bone. Alternatively, it may be implemented as a smaller body having
an outer surface portion which fits the prepared bone surface, and
an inner surface portion rigidly extending in a precise plane
across the prepared bone canal to engage the slotted stem.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will be more fully understood by reference to the
following detailed description when considered in conjunction with
the accompanying drawings, in which:
FIG. 1 illustrates an exploded perspective view of a bone with a
partial break away of a prepared cavity, an alignment guide and an
implant inserted through the alignment guide;
FIG. 2 illustrates a perspective view of the bone, alignment guide
and implant of FIG. 1 with the alignment guide in place and the
implant inserted partially into the bone through the alignment
guide;
FIG. 3 illustrates a perspective view of the alignment guide of the
present invention;
FIG. 4 is a perspective view of an alignment guide of the
invention;
FIG. 5 is a perspective view of the alignment guide of FIG. 4 in
contact with a fluted stem of a hip prosthesis femoral
component;
FIG. 6 is a side view of the alignment guide and fluted stem of
FIG. 5;
FIG. 7 is a cross sectional view of the alignment guide and fluted
stem of FIG. 6 taken along line 7--7;
FIG. 8 is a side view of an alignment guide and prosthetic stem
component of the invention being inserted into a bone;
FIG. 9 is a perspective view of another alignment guide of the
invention:
FIG. 10 is a view of the guide of FIG. 9 engaging a prosthetic
stem;
FIGS. 11A and 11B illustrate stem insertion with the guide of FIG.
9 in a prepared bone; and
FIG. 12 illustrates another alignment guide.
DETAILED DESCRIPTION OF THE INVENTION
The following is a description of a preferred embodiment of the
present invention in use with a hip stem implant. Referring now to
FIGS. 1 through 3, an alignment guide 10 is illustrated. The
alignment guide 10 comprises a body 11, a guide portion 12, and an
opening 14. The body 11 and guide portion 12 form an outer shape
that corresponds to at least a portion of a machined cavity 21 in
the bone 20. The guide portion 12 has an inner circumference 15
having grooves or notches 16 for receiving flutes 31 of the stem 30
an implant 50. Protrusions 13 in the guide portion 12 may contact
the stem 30 of the implant 50. In this embodiment, the grooves 16
and the protrusions 13 form a key for guiding insertion of the stem
30 into the bone cavity. In variations of this embodiment grooves
16, protrusions 13 or the like may be used alone or together to key
insertion of the keyed stem 30.
FIG. 1 illustrates a prepared bone 20 having a machined cavity 21
and a longitudinal cavity 22 formed in the canal of the bone. At
least a portion of the machined cavity 21 has a shape corresponding
to the shape of the alignment guide 10. FIG. 1 further illustrates
an implant 50 comprising a stem 30 having flutes 31 distally
extending along the length of the stem 30; a protrusion or proximal
geometry 32 shaped to fit within the machined cavity 21 of the
bone; and a neck 33 extending from the proximal end of the implant
for receiving a ball portion of a ball and socket joint.
The notches 16 in the inner circumference 15 of the guide are
placed so that when the stem 30 is inserted into the alignment
guide 10, the flutes 31 of the stem 30 fit within the notches 16 in
the alignment guide 10 to hold or guide the stem 30 in an
appropriate or aligned position within the bone cavity.
In this embodiment the shape of the machined bone cavity 21 is
generally tapered to form an elliptical end portion 23. The
alignment guide 10 is similarly shaped with the body 11 forming an
elliptical end portion 18 on the proximal end of the body. The
implant 50 as well includes a similarly shaped proximal section
with an elliptical end portion 34. The bone cavity 21, further
comprises a cut 24 corresponding to tapers 19, 35 on the alignment
guide 10 and the implant 50 respectively. The cut 24 of the bone
cavity 21 and the taper 19 of the alignment guide 10 prevent the
alignment guide 10 from being inserted too far into the bone
cavities 21, 22. The cut 24 of the bone cavity 21 and the taper 35
of the implant 50 similarly prevent the implant 50 from being
inserted too far into the bone cavities, 21, 22 and thus prevent
the neck 33 from being in an improper position.
In use, the alignment guide 10 is inserted into the machined bone
cavity 21 with the elliptical end portion 18 of the alignment guide
10 in alignment with the elliptical end portion 23 of the machined
cavity 21. The stem 30 of the implant 50 is placed in the inner
circumference 15 of the guide portion 12 of the alignment guide 10
with the elliptical end portion 34 of the implant 50 generally in
line with a groove 9 across the elliptical end portion 18 of the
alignment guide 10. In order to insert the implant 50 properly
aligned, the proximal geometry 32 is generally aligned so that it
will fit within the machined bone cavity 21. The flutes 31 are
placed within the notches 16 of the guide portion 12 and the
implant 50 is driven into the bone cavity 22 guided by the
alignment guide 10. When the implant 50 is generally in the bone
cavities 21, 22 but prior to complete insertion, as illustrated in
FIG. 2, the alignment guide 10 is removed by inserting a device
into the opening 14 in the guide 10 to remove it from the bone
cavity 21 and from the stem 30 of the implant 50. The implant 50 is
then further driven into place with the elliptical end portion 34
fitting within the elliptical end portion 23 of the bone and the
taper 35 abutting adjacent a cut 24 of the bone cavity 21.
An additional alignment guide 110 of the invention, illustrated in
FIG. 4, has a handle 112 and an alignment body 114. The handle 112
is generally shaped so as to be easily grasped by a surgeon and has
proximal and distal ends 116, 118. The alignment body 114 is
located at the distal end 118 of the handle 112 and has a guide
surface 120 disposed on an inner portion 122 thereof. The guide
surface 120 is releasably engageable with an outer surface 124 of a
prosthetic stem 126 as shown in FIG. 5.
The illustrated stem 126 is adapted for use as the femoral
component of a hip prosthesis, however, the system of the invention
is useful with a variety of prosthetic implants, especially those
suited for implantation in a long bone. The prosthetic stem 126 may
have proximal and distal portions 128, 130 and have at least one
flute 132 formed on its outer surface 124. The distal portion 130
of the stem 126 is substantially cylindrical and may also include a
slot 134, in particular, a coronal slot. The proximal portion 128
of the stem may have an angled region 136 or proximal spout having
an elliptical cross-section leading to a neck 138. The preparation
of a bone cavity (such as bone cavity 21 of FIG. 1) adapted to such
a geometry is illustrated in U.S. Pat. No. 4,790,852 to Noiles
which is hereby incorporated by reference. A person of ordinary
skill in the art will recognize that other reaming or broaching
techniques may also be used to create a bone geometry corresponding
to the illustrated stem 126.
For use in the present invention, stem 126 has at least one surface
element or keyed component, such as flute 132, disposed on its
outer surface 124 that is angled with respect to the outer surface
124 and extends in the direction of a longitudinal axis 140 (FIG.
6) of the stem 126. As illustrated in FIGS. 1-2 and 6-8, the stem
surface elements may include a plurality of flutes. Generally,
these angled surface features 132 may include any combination of
indentations or protrusions from the outer surface 124 suitable to
hold the stem 126 against rotational misalignment when engaged with
the alignment guide 110.
The guide surface 120 of the alignment guide 110 engages the outer
surface 124 of the stem 126, as shown in FIGS. 4-5, around the
cylindrical stem 126 generally up to about 180.degree.. The guide
surface 120 also includes one or more angled guide surface features
142 which form a key to engage the stem surface features 132 to
hold the stem 126 against rotation. The angled guide surface
features 142 are also formed so that the guide 110 may be removed
from its engagement with the stem 126 in a plane transverse to the
longitudinal axis 140 as illustrated by the lateral axis 144 and
referred to herein as a lateral direction, which, in the
illustrated embodiment, is directed from lateral to medial for a
hip prosthesis embodiment.
In the illustrated embodiment, the outermost guide surface features
142 (FIG. 7) each have an outer angled surface 146 formed to allow
lateral disengagement. That is, rather than contacting a stem
surface feature 132, the outer angled surface 146 is generally in
the direction of the lateral axis 144 so as not to engage a lateral
facing surface 148 of the stem surface element 132, thus permitting
lateral removal of the alignment guide 110 from the stem 126.
In the embodiment illustrated in FIGS. 4 to 8, the alignment guide
110 may have a tapered outer shape 150 to correspond to the shape
of the bone cavity into which the stem 126 is being implanted. The
alignment guide 110 may also have an alignment marker 152 located
on a proximal surface 154 of the guide body 114 to provide a visual
aid for engaging the stem 126 with the alignment guide 110.
A method for inserting a prosthetic stem 126 into a long bone
begins with the preparation of a suitable cavity in the long bone.
Where, as illustrated in FIG. 8, the stem 126 includes features
such as a tapered proximal spout 150, the cavity should be formed
so as to correspond to such features.
The prosthetic stem 126 is placed at the opening of the cavity in
the long bone in a predetermined rotational orientation and is
engaged by the alignment guide 110. The prosthetic stem 126 is
inserted into the cavity while maintaining contact with the
alignment guide 110. A surgeon may apply lateral pressure using the
handle 112 in order to ensure a sufficient engagement between the
prosthetic stem 126 and the alignment guide 110 to prevent
undesired rotation of the stem 126.
The alignment guide 110 may be removed from the stem 126 prior to
final seating of the stem 126 within the cavity. In addition,
surface features such as flutes 132 may be longitudinally extended
in a proximal direction in the area where the guide 110 meets the
stem 126 in order to provide a greater duration of contact between
the stem 126 and guide 110.
Although the alignment guide of the present invention is described
with respect to a particular embodiment, i.e., in use with a fluted
hip stem using the flutes of the stem as a key or reference, it
will be apparent to those skilled in the art that various
modifications may be made without departing from the character and
scope of the invention. For example, the insertion guide may be
used to assist the insertion of any stem like component having a
keyed feature on the outer surface of the stem to key the insertion
of the stem in a properly selected aligned position. The alignment
guide may have any number of indentations or protrusions to key in
the proper insertion of the stem of the implant.
In particular, further embodiments of the insertion may employ a
blade or other protrusion fitted to a slot in the stem to orient
and guide the stem into a fitted insertion position. These
embodiments allow the stem flutes to be optimized for broaching or
cutting a fitted passage and securing the stem to the bone without
requiring the flutes to also sustain shear forces imposed during
insertion by a guiding surface. As seen in FIG. 5, a suitable slot
134 may be already provided on some stems, and this slot is
generally oriented to reduce stem stiffness along one direction,
while allowing some flexibility of fit of the distal stem as it
enters the prepared bone bore.
FIG. 9 illustrates an alignment guide 210 of the invention
configured for slot engagement. In this embodiment, the guide has a
blade 215 which protrudes from one end of a handle 217, which as
illustrated is provided with gripping features such as knurling,
finger grooves or the like. An intermediate portion of the guide
has a surface 219 shaped to nest or fit within the prepared curved
and inclined spout bore of the resected bone end, e.g., against
surface 24 (FIG. 1). Surface 219 thus orients blade 215 along a
central parallel plane. Similarly the prosthesis slot precisely
fits the blade, and is oriented along a central plane of symmetry
of the prosthesis post and shoulder, so that the prosthesis is thus
oriented to seat correctly when fully inserted.
As further illustrated in FIG. 9, the main body of the handle 217
has a distal end face 217a which crosses the handle longitudinal
axis substantially parallel to the bone insertion axis, i.e., at an
angle of about 30.degree. corresponding to the angle between the
bone canal axis and the axis of the prepared bone spout bore. This
allows the prosthesis stem to slide along the blade 215 close to
and substantially parallel to the face 217a, providing maximum
strength, rigidity and precision of the guide mechanism. By way of
example, the thickness of blade 215, and the corresponding stem
slot width, may be on the order of 2-5 millimeters. The handle may
be 10-15 centimeters long, with the blade extending an additional
1-4 centimeters, preferably resulting in a relatively short,
maneuverable guide with a total length under about 14 centimeter.
The guide is advantageously machined or fabricated of a solid
metal, such as titanium or a stainless steel or surgical alloy.
FIG. 10 shows the guide of FIG. 9 in engagement with a prosthesis
stem 230 similar to the stem of FIG. 5. As shown, the blade 215
fits precisely in slot 234, thus aligning and centering the
prosthesis surface 239 with guide surface 219. As the stem is
inserted in bone along an insertion axis A, the blade 215 rides up
the slot 234. Once the stem is securely tracking as it is inserted
in the bone the blade 215 may be withdrawn along the direction of
the handle axis H.sub.i. For ease of withdrawal, the handle has
grip-enhancing features at its proximal end, and is also provided
with a cross-hole 211 (FIG. 9) which may receive a T-bar or be
engaged by an engagement hook of an impact puller, to exert a
withdrawal force along axis H.sub.i.
As noted above, in existing slotted stem prostheses, the slot
serves a compliance function allowing a reduction of bending
stiffness; it may also be compressed as the stem tip is driven in
and subjected to radial compressive force. To prevent binding of
the guide in the stem as the slot is closed, it is therefore
desirable to fabricate the blade or slot with this added
consideration in mind. For example, width dimensions may be set to
initially achieve a slight clearance therebetween, such that as the
distal tip commences to cut its way along the machined bone canal,
the two components acquire a precise fit. Alternatively, the slot
may taper wider toward the stem proximal end to facilitate
withdrawal once the stem has been sufficiently inserted. Similarly,
the blade to stem contact area may be reduced, for example by
hollow-grinding the central face of the blade, so that despite high
compressive forces the blade may slide along the slot and be easily
withdrawn. Furthermore, in conventional prostheses, such as
titanium prostheses, the slot extends only partially up the distal
stem, and this slot length may be inadequate for achieving a
sufficiently stable insert direction before the blade has to be
withdrawn. In the prototype alignment guide shown in FIG. 9, the
distance during which the stem remains precisely guided during
insertion is made long or maximized by positioning the blade
vertically offset along the stem insertion axis--i.e, by having it
project from the lower portion of the handle cross section. This
limitation may also be addressed by providing a slot 234 which
extends further up the prosthesis stem, a procedure which may be
readily implemented for stiffer, stronger prosthesis alloys such as
cobalt chrome. In other embodiments, the distal stem flutes are
made slightly larger in diameter to assure sufficient bite in the
bone canal early in insertion to guarantee straight insertion after
being guided only a short distance by the alignment tool. Thus,
blade offset and stem and slot width and length may each be
adjusted to assure that the blade functions as an effective
guide.
FIGS. 11A and 11B illustrate the use of the alignment guide 210 of
FIG. 9. As shown in FIG. 11A, the guide is nested against the
cylindrical prepared surface of the angularly oriented spout
channel machined in the proximal femur 20, and the prosthesis stem
230 is lowered over the blade 215 while care is taken to visually
align the stem along the axis of the bone. Thereafter, the stem is
driven into the bone, while the blade 215 provides a firm and
precise guide surface, constraining the stem of the prosthesis in
the desired guide plane while allowing straight movement deeper
into the bone canal.
In addition to the embodiment of FIG. 9, the present invention
contemplates an embodiment of the alignment guide wherein a
structure corresponding to the hand-grip portion of the handle is
optional, and , if provided, is a separate element or tool of the
system. In this embodiment, an essential portion of the guide
includes only a body that seats in a defined orientation against
the prepared bone surface, and that possesses a blade protruding
therefrom and positioned across the central plane in which the stem
alignment slot is to be positioned. Such an alignment guide
embodiment 310 is shown in FIG. 12. As seen therein, the guide
possesses a slot-engaging blade 315 that extends radially across
the bone canal from the edge of an arm 316, which in turn extends
downwardly from a positioning body 318. As in the embodiment of
FIG. 1, the positioning body 318 possesses a surface 319 which
aligns against a prepared bone surface. It also has a gripping hole
323 for attaching a handle or extractor to allow removal of the
body 318 along an extraction direction parallel to the spout bore,
after the stem has been inserted to a substantial depth.
This completes a description of the invention and representative
embodiments thereof. Having been thus disclosed, further variations
and modifications will occur to those skilled in the art, and all
such variations and modifications are considered to be within the
spirit and scope of the invention, as defined by the claims
appended hereto and equivalents thereof.
* * * * *